(devel/R-git2r) Updated 0.30.1 to 0.32.0

# git2r 0.32.0 (2023-04-12)

## CHANGES

* Updated the bundled libgit2 source code to version 1.6.3.

* Fix build failure of bundled libgit2 when structure for nanosecond
  type is mssing.

# git2r 0.31.0 (2023-01-26)

## CHANGES

* Removed unused macro 'AC_PROG_CC' from the build configuration
  script.

(mef)